The term "SCSI Enhanced Tape" signifies the Unisys family of SCSI half-inch cartridge tape subsystems adhering to the ANSI SCSI-2 Standard. ANSI refers to the American National Standards Institute. Each SCSI Enhanced Tape drive uses a form of half-inch cartridge media. The 36-Track subsystems use a 3890 and/or 3890 Extended tape.
The 36-Track tape subsystems were introduced in 1993 by vendors such as IBM, Fujitsu, and StorageTek, as an increased capacity replacement for 18-Track tape subsystems. These 36-Track tape subsystems provide the ability to store twice the capacity of a regular 18-Track using the same media, and up to several times the capacity using a new, extended half-inch tape cartridge, assuming that both subsystems utilize data compression.
The SCSI 36-Track tapes involved herein are Unisys tape systems designated as the OST5136, the CTS5236, and the CLU9710-36T tape subsystems. The density requirements directly correlate to the FIPS (Federal Information Processing Standard) CTS5136 subsystems, in that they can read at the 18-Track density, and then either Read or Write at the 36-Track density. The SCSI 36-Track tapes are considered to be compatible with their FIPS counterparts. They are expected to read media written by the FIPS 36-Track or 18-Track subsystems and these FIPS subsystems are considered to be able to read media written by any of the SCSI 36-Track subsystems.
Other tapes involved in the present system are the CLU9710-DLT4 and the CLU9710-DLT7 tapes which were introduced by the Quantum Corporation as a high-performance, high-capacity streaming cartridge tape product. The CLU9710-DLT4 subsystem provides a formatted capacity of up to 40.0 GB on a DLTIV tape and sustained user data transfer rates of 10.0 MB/s assuming compression is being utilized. The CLU9710-DLT7 can provide 70.0 GB capacity under the same circumstances.
These enhanced type SCSI subsystems are being supported via newer Unisys A-Series and NX I/O platforms, for example, those designated as RMM/IOM platforms, and are currently only connected via a Native SCSI channel.
A number of functionalities are being provided in connection with these tape subsystems of which the present focus is that involving statistical data collection. After statistical data collection, an analysis and report is made as will be seen in co-pending U.S. Ser. No. 09/209,983 entitled "System and Method for Analyzing and Reporting Tape Statistics" which is incorporated herein by reference.
Statistical data gathering of a magnetic tape involves identifying various pages supported by the magnetic tape and then selecting certain data to indicate counts of such things as (i) Write errors; (ii) Read errors; (iii) Sequential-Access device information; (iv) Track errors.
The earlier method for gathering statistical data for a tape subsystem (such as the USR 5073) involved tagging an Unload command, and then upon completion of the Unload, issuing a single Log Sense I/O command to retrieve all the available statistical data for the drive. These internally stored statistics are cleared as result of a Log Select I/O command. The problem with this method is two fold; 1) SCSI Enhanced Tape drives do not necessarily support a page code designated "Return All Supported Pages"-- which would not allow all the statistics to be retrieved with a single I/O; and 2) the tape drive's internally stored statistical data is cleared as a direct result of an "Unload" which would result in "just-cleared" statistics being retrieved with the pre-existing algorithm. Thus, this prior algorithmic method was never sufficient to gather the required statistical data for SCSI Enhanced Tapes.
One of the SCSI Enhanced tape drives, designated the "OST5136," does support a "Return All Supported Pages" page. However, the volume amount of information it returns is prohibitive since it requires a huge buffer dimension. Here, the buffer required would be significantly larger than the standard buffer required to piece together the data returned for each page, when each page is requested individually.
The present method and system provides a new algorithmic arrangement, whereby a new procedure designated "COLLECT_TAPE_STATS" is called out of the procedure, "REWINDIT", prior to issuing an Unload I/O. This new procedural method, while using another new procedure designated "COLLECT_LOG_SENSE_DATA", handles the collection and logging of the desired statistical data. Afterwards, and completely independently of the statistical data gathering, the "Unload" I/O is issued as requested by the user.
In addition to being called when an Unload I/O is performed, COLLECT_LOG_SENSE_DATA is also invoked when the tape drive notifies the system that its statistical data buffers are getting ready to "overflow." The software is notified of this overflow condition via a "Check Condition" status, which is translated into a Logical Result Descriptor value (LRD id) of LRDLOGCOUNTEROVERFLOWID. Then, an initial error handling routine designated "TERMINATEIOOPERATION" defers the actual tape error handling to a routine "HANDLEMAGTAPEEXCEPTION" (HMTE). The routine HMTE then calls COLLECT_LOG_SENSE_DATA to issue the appropriate sequence of I/Os to collect all of the required statistical data and append this information to the Input/Output Control Block (IOCB) associated with the overflow error condition before writing the statistical data to the SYSTEM/SUMLOG file.
The new procedure designated COLLECT_TAPE_STATS is a Master Control Program (MCP) procedure called by REWINDIT prior to a tape being unloaded. COLLECT_TAPE_STATS is a jacket procedure for the new MCP procedure COLLECT_LOG_SENSE_DATA. Its purpose is to put the tape unit in an expected state before calling COLLECT_LOG_SENSE_DATA and to return it to its initial state after the call.
The COLLECT_LOG_SENSE_DATA is a Master Control Program (MCP) procedure which is called through the procedure COLLECT_TAPE_STATS for REWINDIT when a tape is to be unloaded. Its purpose is to collect and store a SCSI Enhanced Tape's statistical data as returned by a sequence of SCSI Log Sense I/O Commands. An initial Log Sense command to retrieve page "00" is issued to determine the drive's "supported pages". The number of pages involved corresponds to the number of Log Sense I/Os to be issued to the tape drive. After all of the data is assembled, it is written to and stored in the SYSTEM/SUMLOG file (i.e., the SUMLOG) so that subsequent analysis of the statistical information can be performed as needed.